1. Field of the Invention
The present invention relates to a charging system, a charging device, and a method for controlling the same and, more particularly, to charging devices sharing power with each other.
2. Description of the Prior Art
Increasing attention to environments has been followed by extensive development of automobiles that move using electric energy. Such automobiles include electric automobiles, which are solely powered by electricity, and hybrid-type automobiles, which include both gasoline engines and electric motors.
In order for an automobile to run using electric energy, it requires a device capable of supplying it with electric energy. In the case of a fuel cell automobile, electricity, which is generated in the course of coupling between hydrogen and oxygen, is used to supply energy needed to run the automobile. The fuel cell is a kind of generator and is capable of continuously generating electric energy when supplied with fuel (e.g. hydrogen). However, an automobile that does not include such a generator as the fuel cell needs to be supplied with electric energy using an electric energy storage device, such as a battery.
A battery is a device capable of converting chemical energy into electric energy; it converts electric energy into a chemical structure in a high-energy state, through a charging process, and stores it; and it converts the chemical structure in a high-energy state into a chemical structure in a low-energy state, through a discharging process, and emits energy, which is generated through the conversion, as electric energy. Electric automobiles and hybrid automobiles employ such batteries as electric energy supply sources.
Such batteries can store only a limited amount of energy, so that automobiles need to charge their batteries frequently. Charging devices for charging automobiles, which include batteries, or charging systems, which include at least two charging devices, have recently been installed at a number of locations.
Charging systems, which include one charging device or at least two charging devices, are supplied with power from a commercial power grid, such as a system, and convert the supplied power in conformity with the voltage and characteristics of automobiles. However, there is a limit on the amount of power that can be supplied from the system to such charging devices or charging systems. Such limits largely occur in terms of hardware and policy. In terms of hardware, first, hardware devices such as a power line (cable), a circuit breaker, and a transformer have a predetermined power capacity at a contact point, which connects a charging device or a charging system with the system. Such a hardware-related limit on power capacity places a limit on the amount of power that can be supplied from the system to a charging device or a charging system.
In terms of policy, which is another aspect, a similar limit may occur. The process of charging automobiles instantly require a large amount of power, and, in terms of the system's management, such power peaks may be factors that disturb the system. For this reason, the policy-making authorities may limit the amount of power, which is supplied through a contact point leading to the system, as a policy. Such a limit can be placed by a power limiter, or through a price polity (e.g. a policy of applying a higher unit price to the amount of power consumption that exceeds a predetermined limit).
The above-mentioned limit on power supply may be a factor that interferes with efficient operation of a charging device or a charging system. It will be assumed for example that two charging devices are installed in a charging system, a number of automobiles are connected to charging device B among them, and no automobile is connected to charging device A. Then, the limited power capacity may prevent charging device B from supplying sufficient charging power to the connected automobiles. The situation in which only limited power is supplied to charging device B, while charging device A has sufficient amount of available power, is inefficient in terms of operation of the charging system.
On the other hand, besides the limit on power supply, the division of charging devices into slow charging devices and rapid charging devices is another factor that interferes with efficient operation of a charging device or a charging system. It will be assumed for example that one slow charging device and one rapid charging device are installed in a charging system. When a first automobile has already been connected to the fast charging device, a second automobile needs to be connected to the slow charging device. However, in order to rapidly charge the second automobile after charging of the first automobile is completed, the second automobile needs to be disconnected from the slow charging device and then reconnected to the rapid charging device, which is inconvenient. If the connection is not changed in this manner, the second automobile needs to continuously receive charging power from the slow charging device only until charging is completed, which lengthens the charging time. Such a division of charging devices into slow charging devices and rapid charging devices results in inconvenient change of charging connection of the following automobile or inefficient charging, which uses the slow charging device even when the rapid charging device is available.